The subject matter herein relates generally to casting objects using a casting operation.
The steel railway wheels are manufactured during a casting operation wherein molten steel is poured into a machined graphite mold. The mold typically includes a top half or cope that is usually a graphite block and a bottom half or drag that is also usually a graphite block. The top portion or front face of the object being cast is machined in the cope and the bottom portion or rear face of the object being cast is machined in the drag. The mold includes sections that form a hub, plate and rim of the railway wheel. When the cope section and drag section are combined to form a complete mold, such complete mold is positioned at a pouring station wherein molten steel is poured into the cavity in the mold to form the hub, plate and rim of the railway wheel.
In some known assemblies, a central riser is provided in the cope section of the mold such that additional molten metal can be held as necessary to downwardly fill into the mold during cooling and solidification of the railway wheel just after pouring. There are accepted standards for porosity of steel railway wheels that must be met by designing the central riser to hold an adequate volume of metal to fill downwardly into the molds during cooling and solidification of the wheel. Upon filling of the mold cavity and central riser, the metal pouring is stopped and the graphite mold is then moved from the pouring station allowing sufficient time for the steel to solidify before the cope and drag sections are separated.
In a machined graphite mold, the graphite absorbs heat from the molten steel in a manner such that the molten wheel is fairly rapidly cooled and solidified at the outer surface in contact with the graphite. This allows a high production rate of wheels as the cope and drag can be fairly quickly separated from each other shortly after pouring thereby allowing the wheel to be properly cooled and otherwise heat treated during its manufacture. Due to the rapid absorption of heat from the molten steel by the graphite mold, it is current practice to provide a thick plate between the hub and rim to ensure that the center of the plate remains molten for a sufficient amount of time to allow the excess molten metal in the central riser to flow from the hub, through the plate and to the rim to achieve the desired porosity in the railway wheel. The added thickness of the plate adds to the overall weight of the railway wheel. The extra material of the plate may be later machined away, but this process adds time and cost to the manufacturing process.
It is desirable to decrease the amount of material in the plate, but still allow the plate to remain molten long enough to achieve the desired porosity of the cast steel railway wheel.